This invention relates generally to filters for filtering and separating fluids. More particularly, the present invention relates to fuel filters for removing foreign particles and separating water from the fuel of the fuel supply system of an internal combustion engine.
Diesel fuel supplies frequently contain significant quantities of abrasive particles and water which present the potential for permanent damage to the components of the fuel injection pump, the fuel delivery system and the engine. Consequently, an effective fuel filter as a practical necessity is conventionally incorporated into the fuel supply system of a diesel engine. A multitude of conventional fuel filters employ a disposable filter cartridge which is replaced at pre-established intervals of filter usage. Such fuel filters perform the dual function of removing particulate material from the diesel fuel and separating water from the fuel.
U.S. Pat. Nos. 4,976,852 and 5,084,170, which are assigned to the assignee of the present invention, disclose fuel filter assemblies to which the present invention relates. The fuel filters employ a base which mounts a disposable filter cartridge. In some disclosed embodiments, the cartridge includes a dual stage filter system wherein fuel flows axially to a primary filter element for removing particulate matter and coalescing water droplets and axially to a second filter stage which functions as a water barrier. Filtered fuel flows axially and exits through an outlet passage of the base. The water may be collected in a sump and periodically removed. The cartridge is secured to the base by a collar which engages against a roll seam structure of the cartridge.
For most, if not all diesel fuel delivery systems, air pockets are present in the fuel filter as fuel circulates through the fuel filter. The air pockets normally form at the top of the fuel filter. Air bubbles tend to form in the fuel circulating through the filter due to the air pockets. For pressurized fuel delivery systems, the air pockets tend to disintegrate over time and/or the stream of bubbles present in the fuel is of a relatively small magnitude. The air pockets do not result in the formation of large air bubbles in the fuel supply partly due to the vapor pressure of the pressurized fuel. Consequently, for pressurized systems, air pockets in the fuel filter do not present a significant problem or obstacle to the circulation of fuel through the fuel filter and the delivery of fuel to the engine.
However, in vacuum applications, the formation of air pockets in the fuel circulating through the filter can present a more significant problem. The air pockets are much more resistant to absorption over time in vacuum systems. Moreover, the vacuum suction exerted on the fuel tends to result in ingestion of larger air bubbles which can become an obstacle to uniform fuel delivery to the engine. The air pockets may grow as a result of changing levels of fuel within the filter. The fuel level changes may be caused by vehicle maneuvering, such as turning, which produces centrifugal forces that result in sloshing of fuel within the filter. The air pockets within the filter may also enlarge over time under a vacuum system. Vacuum systems tend to be more susceptible to the ingestion into the fuel delivery stream of an air bubble which has a magnitude sufficient to produce a subsequent engine sputter.